Organic electro-luminescent devices are well known. Organic electroluminescent (EL) devices are electronic devices that emit light in response to an applied potential. In simplest form, an organic EL device is comprised of an anode for hole injection, a cathode for electron injection, and an organic medium sandwiched between these electrodes to support charge recombination that yields emission of light. These devices are also commonly referred to as organic light-emitting diodes, or OLEDs.
Organic light-emitting diode (OLED) technology incorporates organic luminescent materials that, when sandwiched between electrodes and subjected to an electric current (AC or DC), produce intense light of a variety of colors. These OLED structures can be combined into the picture elements or pixels that comprise a display, such as flat-panel displays in watches, telephones, laptop computers, pagers, cellular phones, calculators, and the like. OLEDs are also useful in a variety of applications as discrete light-emitting devices.
Optically excited organic dye lasers, in the liquid state, are well-known sources of powerful and highly coherent tunable laser emission. Two references which describe such lasers are: (1) F. P. Schäfer (ed.), Dye Lasers (Springer, Berlin, 1990), and (2) F. J. Duarte (ed.), High Power Dye Lasers (Springer, Berlin, 1991).
While such lasers can be powerful, these lasers can be rather large and complex and their attractiveness diminishes for many low power applications.
Recently, organic dye lasers have made a successful transition into the solid-state using highly homogeneous gain media comprised of dye-doped polymers. References which describe these developments include: F. J. Duarte, Appl. Opt. 33, 3857 (1994).; A. Maslyukov, S. Solokov, M. Kaivola, K. Nyholm, and S. Popov, Appl. Opt. 34, 1516 (1995); and A. Costela, I. Garcia-Moreno, and R. Sastre, Phys. Chem., Chem. Phys. 5, 4745 (2003).
Multiple-prism grating tunable laser oscillators, using dye-doped organic matrices, have been reported to yield nearly diffraction limited laser beams and single-longitudinal-mode emission at power levels in the kW regime. Refer to F. J. Duarte, Appl. Opt. 38, 6347 (1999).
Although these may be attractive for some applications, these lasers still require another laser as source of excitation. In this regard, it would be technologically advantageous to have semiconductor organic sources of coherent radiation excited directly by electrical means. Optically excited organic semiconductor films have been reported to lase by several authors. See, for example, S. Riechel, U. Lemmer, J. Feldman, S. Berleb, A. G. Mückl, W. Brütting, A. Gombert and W. Wittwer, Opt. Lett. 26, 593 (2001); and W. Holzer, A. Penzkofer, T. Pertsch, N. Danz, Abräuer, E. B. Kley, H. Tillmann, C. Bader, and H. H. Hörhold, Appl. Phys. B. 74, 333 (2002). See also Heeger and Bradley R. Xia, G. Heloitis, D. D. C. Bradley, Applied Physics Letters, 82 3599 (2003); and G. Heliotis, D. D. C. Bradley, G. A. Turnbull and I. D. W. Samuel, Applied Physics Letters, 81 415 (2002). A further reference is M. D. McGehee, M. A. Díaz-García, F. Hide, R. Gupta, E. K. Miller, D. Moses, and A. J. Heeger, Applied Physics Letters, 72, 13 1536 (1998).
As such, the subject of direct electrical excitation of organic lasers has been an issue discussed, for some time, in the open literature. For example, see: G. Kranzelbinder and G. Leising, Rep. Prog. Phys. 63, 729 (2000); V. G. Kozlov, P. E. Burrows, G. Parthasarity, and S. R. Forrest, Appl. Phys. Lett., 74, 1057 (1999); and M. A. Baldo, R. J. Holmes, and S. R. Forrest, Phys. Rev. B., 66, 35321 (2002).
It has been recognized that two of features of laser radiation are directionality of the emission, that is, low beam divergence, and spectral coherence, also known as narrow-linewidth emission. Therefore, any incipient study of a potential electrically excited organic laser must include these two basic parameters.
Accordingly, there exists a need for a direct electrical excitation of an electrically driven organic laser which provides for low beam divergence and spectral coherence.
The present invention provides an electrically driven organic laser which provides for low beam divergence and spectral coherence.